1. Field of the Invention
Aspects of the present invention relate to a fuel processor that reforms a fuel to be suitable for supplying to a fuel cell, and particularly, to a fuel processor having a CO removal apparatus that has an improved warming-up structure and a method of operating the fuel processor.
2. Description of the Related Art
A fuel cell is an electrical generator that changes chemical energy of a fuel into electrical energy through a chemical reaction, and can continuously generate electricity as long as the fuel is supplied. FIG. 1 is a schematic drawing illustrating the energy transformation structure of a fuel cell, and FIG. 2 is a block diagram showing a configuration of a conventional fuel processor that processes a fuel that is to be supplied to a fuel cell. Referring to FIG. 1, when air that includes oxygen is supplied to a cathode 1 and a fuel containing hydrogen is supplied to an anode 3, electricity is generated by a reverse electrolysis reaction as water and protons move through an electrolyte membrane 2. However, a unit cell 4 does not generally produce a useful high voltage. Therefore, electricity is generated by a stack 20 (referring to FIG. 2) in which a plurality of unit cells 4 are connected in series.
A hydrocarbon group containing material such as a natural gas can be used as a fuel source for supplying hydrogen to the stack 20. Hydrogen is often extracted from a fuel source in a fuel processor 10, as depicted in FIG. 2, in order to supply hydrogen to the stack 20.
The fuel processor 10 includes a desulfurizer 11, a reformer 12, a burner 13, a water supply pump 16, first and second heat exchangers 14a and 14b, and a CO removal unit 15. The CO removal unit 15 comprises a CO shifter 15a and a CO remover 15b. The hydrogen extraction process is performed in the reformer 12. That is, hydrogen is generated in the reformer 12, through a chemical reaction 1 indicated below between a hydrocarbon group containing gas, that acts as the fuel source, entering from a fuel tank 17, and steam entering from a water tank 18, by the action of a water supply pump 16. The reformer 12, is heated by the burner 13.CH4+2H2O→CO2+4H2  [Chemical reaction 1]
However, during the reaction, CO is generated, as well as CO2, as a byproduct. If a fuel containing CO of 10 ppm or more is supplied to the stack 20, electrodes in the stack are poisoned, thereby greatly reducing the performance of the fuel cell. Therefore, the content of CO in an outlet of the reformer 12 is controlled to be 10 ppm or less by installing the CO shifter 15a and the CO remover 15b. 
Chemical reaction 2, as indicated below, occurs in the CO shifter 15a, and chemical reactions 3, 4, and 5, as indicated below, occur in the CO remover 15b. The CO content in the fuel that has passed through the CO shifter 15a is 5,000 ppm or less and the CO content in the fuel that has passed through the CO remover 15b is reduced to 10 ppm or less.CO+H2O→CO2+H2  [Chemical reaction 2]CO+½O2→CO2  [Chemical reaction 3]H2+½O2→H2O  [Chemical reaction 4]CO+3H2→CH4+H2O  [Chemical reaction 5]
The desulfurizer 11 located at an inlet of the reformer 12 removes sulfur components contained in the fuel source. The sulfur components are absorbed while passing through the desulfurizer 11 because the sulfur components are very detrimental to the electrodes. Even if a sulfur component of 10 parts per billion (ppb) or more is supplied to the stack 20, electrodes can easily be poisoned.
When the fuel processor 10 is operating, a fuel source such as a natural gas is supplied to the reformer 12, through the desulfurizer 11, from the fuel tank 17. A portion of the fuel source is used as a fuel for igniting the burner 13. Then, steam that has entered through the first and second heat exchangers 14a and 14b reacts with the desulfurized fuel source, in the reformer 12, in order to generate hydrogen. The generated hydrogen is supplied to the stack 20 after the CO content is reduced to 10 ppm or less, while passing through the CO shifter 15a and the CO removal unit 15b. 
When the fuel processor 10 starts after a long shutdown, the reformer 12 and the CO shifter 15a have cooled down to room temperature. With the reformer 12 and the CO shifter 15a at room temperature the fuel processor 10 is unable to instantly go into a normal operating condition, but can only perform normally after a few hours of heating. At this point, the temperature of the CO shifter 15a is more problematic as compared to the reformer 12. That is, the temperature of the reformer 12 can be increased to a desired level in a short time by directly heating it with the burner 13, but the CO shifter 15a requires additional time to reach a normal operating temperature because the CO shifter 15a is indirectly heated by gases entering from the reformer 12. A typical normal operating temperature of the reformer 12 is approximately 700° C., and a typical normal operating temperature of the CO shifter 15a is approximately 200° C. However, it takes only approximately 20 minutes for the reformer 12 to reach 700° C. after starting, but it takes approximately one hour for the CO shifter 15a to reach 200° C. Accordingly, although the reformer 12 has reached its normal operating temperature, the fuel processor 10 is unable to operate until the CO shifter 15a reaches its normal operating temperature. In other words, hydrogen gas can be produced in the reformer 12 in approximately 20 minutes after the start of the fuel processor 10, but in order to reduce the CO component in the gas below 5,000 ppm, the fuel processor 10 must wait one hour for the CO shifter to reach its normal operating temperature.
Accordingly, in order to reduce the time from starting to normal operation of the fuel processor 10, there is a need to develop a method of preheating the CO shifter 15a. 